For their growth and development, plants require sunlight, moisture, oxygen, and minerals. External factors are required. The growth and development of plants are regulated by a variety of intrinsic factors as well. We call these phytohormones. Plants produce and transmit these hormones in almost every part of the plant. Plant growth hormones may act synergistically or individually. Each hormone may play a complementary or antagonistic role. As well as extrinsic factors, hormones are involved in processes such as vernalization, phototropism, seeds germination, dormancy, and so forth. Controlled crop production is achieved through the exogenous application of plant hormones. Charles Darwin first observed phototropism within the coleoptiles of canary grass, and Frederick Going isolated auxin for the first time from the coleoptiles of oat seedlings.

(Image Will be Updated Soon)

Which of the Following is a Plant Hormone?

A phytohormone is a chemical compound found in very low concentrations in plants. There are derivatives of indole (auxins), terpenes (Gibberellins), adenine (Cytokinins), carotenoids (Abscisic acid), and gases (Ethylene) and also examples of plant hormones.

What are the Two Types of Plant Hormones?

The growth and development activities of plants are controlled by hormones such as cell division, enlargement, flowering, seed formation, dormancy, and abscission.

There are two main types of plant hormones based on how they act:

Growth Promoters for Plants
Growth inhibitors for plants

Plant Hormones and Their Functions

Auxin Hormone

To grow is what auxin means. Agricultural practices and horticultural practices use auxins extensively. The majority of them reside at the growing apices of roots and stems before migrating to other parts of the plant.

Naturally: Indole-3-acetic acid (IAA), Indole butyric acid (IBA)
Synthetically: 2,4-D (2,4-Dichlorophenoxyacetic acid), NAA (Naphthalene acetic acid)

Functions:

Roots and stems lengthen as a result of cell division.
The growth of lateral buds is inhibited by apical dominance and IAA in apical buds.
It is inhibited by apical dominance and IAA in the apical buds that lateral buds grow.
Ensures that leaves, flowers, and fruits do not fall prematurely.

Gibberellins Hormone

Gibberellins are acidic compounds found in higher plants and fungi (GA₁, GA₂, GA₃,....). There are more than 100 kinds of gibberellins (GA₁, GA₂, GA₃,...) known.

Functions:

Bolting in rosette plants like cabbage, beet induces sudden elongation of the internodes just before flowering.
Delays senescence.
Induces parthenocarpy.
Elongates the stem and reverses dwarfism.

Cytokinins Hormone

Plants produce cytokinins when rapid cell division occurs, for example, at roots apices, shoot buds, young fruits, etc. The movement of cytokinins is basipetal and polar.

Naturally: Zeatin (corn kernels, coconut milk), isopentenyl adenine
Synthetically: Kinetin, benzyladenine, diphenylurea, thidiazuron

Functions:

In cultures, it promotes the growth of lateral and adventitious shoots and is used to initiate the growth of shoots
Assists in overcoming apical dominance caused by auxin
Leaf chloroplasts should be stimulated
Activates nutrients and delays leaf senescence

Abscisic Acid Function

Inhibiting plant growth regulates abscission and dormancy, affects plant metabolism, and increases plant tolerance to stress. It's also called the "stress hormone" because it increases plant tolerance to stress.

Functions:

Leaf abscission and fruit abscission caused by this plant
Inhibition of seed germination
Senescent leaves are induced
Do not affect seeds' dormancy, so it is useful for storing seeds

Ethylene Plant Hormone

It regulates many physiological processes and is one of the most widely used agricultural hormones, acting as both a growth promoter and an inhibitor. It is produced in gaseous form by ripening fruits and tissues during senescence.

Functions:

Fruits ripen more quickly when it is present
Leaves become less epinasty
Breaks dormancy of seeds and buds
Enhances the rapid extension of petioles and internodes

Besides the main 5 hormones, other hormones also affect the physiology of plants, such as brassinosteroids, salicylates, jasmonates, strigolactones, etc., are the other examples of plant hormones in the study of the application of plant hormones. In this way, plant hormones and their functions are described.

Did You Know

The oilseeds, pulses, and cereal crops each requires specific plant growth hormones.
By producing auxins and cytokinins as examples of plant hormones, plants can grow stronger, root and shoot growth can be promoted, and stress can be reduced.

Want to read offline? download full PDF here

Download full PDF

Is this page helpful?

FAQs on Plant Hormones and Their Role in Plant Growth and Development

1. What are plant hormones?

Plant hormones are chemical messengers that regulate growth, development, and responses to stimuli in plants. These organic compounds are produced in small amounts and transported to target tissues where they control specific physiological processes. Major plant hormones include:

Auxins – promote cell elongation and apical dominance
Gibberellins – stimulate stem elongation and seed germination
Cytokinins – promote cell division
Ethylene – regulates fruit ripening
Abscisic acid (ABA) – controls stress responses and seed dormancy

They are also called phytohormones and are essential for coordinating plant life processes.

2. What are the five major types of plant hormones?

The five major types of plant hormones are auxins, gibberellins, cytokinins, ethylene, and abscisic acid. These primary phytohormones function as follows:

Auxins – cell elongation, apical dominance, root initiation
Gibberellins – stem growth, flowering, seed germination
Cytokinins – cell division, delay of leaf senescence
Ethylene – fruit ripening, leaf abscission
Abscisic acid (ABA) – stomatal closure, seed dormancy, stress tolerance

Together, they regulate plant growth and development in a coordinated manner.

3. What is the function of auxin in plants?

Auxin primarily promotes cell elongation and controls directional growth in plants. The main natural auxin is Indole-3-acetic acid (IAA). Its key functions include:

Stimulating cell elongation in stems
Maintaining apical dominance
Initiating adventitious root formation
Regulating phototropism and gravitropism

Auxin is mainly produced in the shoot apex and transported downward to other plant parts.

4. How does gibberellin affect plant growth?

Gibberellin stimulates stem elongation, seed germination, and flowering in plants. These gibberellins (GA) promote growth by increasing cell division and cell elongation. Major roles include:

Breaking seed dormancy and activating enzymes like amylase
Increasing internode length
Inducing flowering in some long-day plants
Enhancing fruit growth

Gibberellins are especially important in early plant development.

5. What is the role of cytokinins in plants?

Cytokinins promote cell division and delay aging in plant tissues. These hormones are mainly synthesized in the roots and transported upward. Their major functions include:

Stimulating cytokinesis (cell division)
Delaying leaf senescence
Promoting lateral bud growth by counteracting auxin
Enhancing nutrient mobilization

Cytokinins work in balance with auxins to regulate organ formation.

6. Why is ethylene called a gaseous plant hormone?

Ethylene is called a gaseous plant hormone because it exists and diffuses as a gas under normal conditions. Unlike other plant hormones, ethylene (C₂H₄) is a simple hydrocarbon gas. Its key roles include:

Accelerating fruit ripening
Promoting leaf and fruit abscission
Inducing senescence
Helping plants respond to stress

Its gaseous nature allows it to act quickly and spread easily between plant tissues.

7. What is the function of abscisic acid (ABA) in plants?

Abscisic acid (ABA) primarily regulates stress responses and induces seed dormancy in plants. Known as the stress hormone, abscisic acid (ABA) performs the following functions:

Causing stomatal closure during water stress
Maintaining seed dormancy
Inhibiting growth under unfavorable conditions
Enhancing drought tolerance

ABA ensures plant survival during environmental stress.

8. How do plant hormones control plant growth and development?

Plant hormones control growth and development by coordinating cell division, elongation, and differentiation in specific tissues. They act through signaling pathways that regulate gene expression. The control occurs through:

Production in specific organs (e.g., shoot tips, roots)
Transport to target cells
Binding to specific receptors
Triggering physiological responses

The interaction between auxins, gibberellins, cytokinins, ethylene, and ABA ensures balanced plant growth.

9. What is the difference between auxin and cytokinin?

Auxin mainly promotes cell elongation, while cytokinin primarily stimulates cell division. The key differences between auxin and cytokinin are:

Main function: Auxin – cell elongation; Cytokinin – cell division
Site of synthesis: Auxin – shoot apex; Cytokinin – root tips
Effect on buds: Auxin maintains apical dominance; Cytokinin promotes lateral bud growth

The ratio of auxin to cytokinin determines organ formation in plant tissue culture.

10. Can you give examples of plant hormone applications in agriculture?

Plant hormones are widely used in agriculture to improve crop yield, growth, and fruit quality. Common applications of plant growth regulators include:

Using auxins to promote root formation in cuttings
Applying gibberellins to increase fruit size in grapes
Spraying ethylene to accelerate fruit ripening
Using cytokinins in tissue culture for shoot formation

These practical uses make plant hormones essential in modern horticulture and crop production.